Crash with native QComboBox in refreshing QWidget

When using a native QComboBox on macOS, Qt will simulate a mouse click on the original button per the comment in qcombobox.cpp:

// The Cocoa popup will swallow any mouse release event.
// We need to fake one here to un-press the button.

If the selection of a value in the combobox triggers a refresh of the Widgets, effectively removing the source of the native combobox, this can lead to a crash because the original Widget has been deleted already:

QMouseEvent mouseReleased(QEvent::MouseButtonRelease,
                          q->pos(),
                          q->mapToGlobal(QPoint(0, 0)),
                          Qt::LeftButton,
                          Qt::MouseButtons(Qt::LeftButton),
                          {});
[..]
QPoint result = data->crect.topLeft(); // data is NULL already
[..]
{ return QPoint(x1, y1); }             // inline function will crash because x1 does not exist

In the application I ran into this a selection of a combobox triggers a refresh and calls widget->deleteLater(); on the parent widget, which works most of the time but in some cases the change of the combobox value happens before the mouseRelease event can be simulated.

If the code were to check if the originating Widget actually still exists and is a valid widget (QWidgetData is NULL) before simulating the mouse event, the crash could be avoided.